This application claims the priority of 198 44 212.2, filed in Germany on Sep. 26, 1998, and PCT/EP99/06342 filed in Europe on Aug. 28, 1999, the disclosures of which are expressly incorporated by reference herein.
The invention relates to a control method for a supercharged internal combustion engine.
German Reference DE 40 25 901 C1 discloses an exhaust gas turbocharger for an internal combustion engine which has a turbine with a turbine geometry which can be variably set via a variable turbine guide vane, and a compressor, driven by the turbine, for raising the supercharging pressure in the cylinder inlet. The turbine guide vane can be adjusted with the aid of an actuator so as to vary the active cross section of the turbine. It is possible therefore, depending on the operating state of the internal combustion engine, to implement exhaust back pressures at various levels in the section between the cylinders and the exhaust gas turbocharger, as a result of which the output of the turbine and the power of the compressor can be adjusted depending on need. The turbine guide vane is controlled to a desired supercharging pressure in accordance with prescribed characteristic lines.
In order to achieve an improvement in efficiency with simple means in a non-stationary operation of the internal combustion engine, the supercharging pressure is controlled below and above a threshold value for the exhaust back pressure in accordance with different characteristic lines. It is possible thereby to prevent the occurrence of uncontrolled pressure rises in the exhaust pipe upstream of the turbine after a positive load change during the rise in supercharging pressure. The internal combustion engine need no longer emit against a raised exhaust back pressure, and the efficiency is raised.
The supercharging pressure of such internal combustion engines is frequently adjusted to the desired value with the aid of a supercharging pressure controller implemented as a PID controller, the supercharging pressure controller applying the required control signal to an adjustable supercharger component influencing the supercharging pressure. Since the supercharging pressure substantially influences the vehicle operation in the activated drive operating mode and, in particular in the case of heavy commercial vehicles, also in engine braking operation, the functionality of the controller and/or of the components participating in the control must be regularly checked.
The invention is based on the problem of monitoring the control of supercharging pressure in a supercharged internal combustion engine with the aid of simple means and, if appropriate, displaying a malfunction.
The novel control method uses a PID controller for adjusting the desired supercharging pressure. The integration component of the PID integration element usually increases continuously with time. According to the invention, this integration component is now compared with a tolerance band which is prescribed with a tolerance value at either end as an ideal integrator mean value. If the integration component exceeds or falls below the tolerance band, a defective operating state is present, and a fault signal is produced to assist in the identification of the defective state during the controlling of the supercharged internal combustion engine. This defective state can be classified as a fault of low severity as long as only the integration component is outside the tolerance band, but otherwise the system deviation of the integration element is still approximately zero, which means the PID controller is still capable of controlling to the prescribed desired supercharging pressure value.
This method has the advantage that faults can be identified clearly and reliably in running operation without additional measures such as, for example, workshop interventions with additional test procedures.
In a particularly advantageous way, the method includes the use of a PID controller and a system deviation is detected by comparison with a limit value and used to generate a fault signal. This defective state can be classified as a severe fault, since a remaining system deviation which is not allowed to occur with the use of an integration element in the case of a correct mode of operation renders it impossible to set the desired supercharging pressure.
The combination of monitoring the integration error and the system deviation represents a complete safety concept which manages without additional outlay on hardware, such as sensors or the like, and can be implemented with a low outlay. In this case, the monitoring can be performed in two stages, firstly by checking the integration component in a first stage, and in a second stage also checking the system deviation for the case when the integration component is outside the permitted range.
In the case of a fault, a fault signal is generated and expediently input into the engine regulation and control system of the internal combustion engine. Both in the case of a fault in the first stage and in the case of a fault in the second stage, a fault signal is generated in each case, it advantageously being possible to differentiate the type of fault via specific markings of the fault signals.
The derivative-action element of the PID controller can be set to zero if appropriate. The controller reduces to a PI controller in this case.
The control method is preferably used in combination with an exhaust gas turbine with variable turbine geometry which can be used to control the supercharging pressure by adjusting the variable control device of the turbine geometry in accordance with prescribed supercharging pressure characteristic diagrams up to the setting of the desired supercharging pressure.